Generally, balance is the ability to maintain the line of gravity of a body within the base of support with minimal postural sway. Sway is the horizontal movement of the centre of gravity or mass, which can occur in the anterior-posterior or medial-lateral directions. A person's balance can be impaired due to conditions, such as aging, concussion, stroke, spinal cord injury, Parkinson's disease, multiple sclerosis, or the like. Currently, center of pressure measured from a force plate is considered the gold standard measure of balance. However, force plates and associated measurement systems tend to be quite large, non-portable, and expensive.